We propose to construct detailed physical maps of in vitro synthesized double-stranded DNA made from AKR, NZB (xenotropic) and Moloney mouse sarcoma virus. We would like to make DNA fragments specific for each virus and use them to determine the number and location of viral DNA copies integrated in the cell genome. We plan to continue our heteroduplex studies using Moloney mink cell focus-forming virus (M-MCF), AKR-MCF, Abelson leukemia virus and several sarcoma viruses. In addition, we plan to study the homology and structure of viral specific mRNAs by forming heteroduplexes with full genome length cDNA transcripts. We will determine the nucleotide sequence of the 3'-end of the genome by making cDNA 3'. We propose to sequence other regions of the genome.